<PAGE>


                                                                   EXHIBIT 10.15

                                                                  CONFORMED COPY



                             CONTRIBUTION AGREEMENT



            THIS CONTRIBUTION AGREEMENT, dated as of December 26, 2001, is
entered into among AMTROL Holding Inc., a Delaware corporation ("HOLDING"),
AMTROL Inc., a Rhode Island corporation ("AMTROL"), Water Soft Inc., a Rhode
Island corporation ("WATER SOFT" and, together with AMTROL, each individually a
"BORROWER" and collectively the "BORROWERS"), and certain subsidiaries of the
Parent identified on the signature pages hereof as Guarantor (together with
Holdings each a "GUARANTOR" and collectively the "GUARANTORS").

                              W I T N E S S E T H :

            WHEREAS, contemporaneously herewith, Borrowers, Guarantors, Cypress
Merchant Banking Partners, L.P. ("CMBP") and Cypress Offshore Partners, L.P.
("COP"; together with CMBP, the "Lenders") are entering into that certain Loan
Agreement dated as of December 26, 2001 (as amended, restated, supplemented, or
otherwise modified from time to time, the "LOAN AGREEMENT");

            WHEREAS, Borrowers are jointly and severally liable for the
repayment of the Obligations (as defined in the Loan Agreement) owing by
Borrowers to the Lenders under the Loan Agreement and each of the other Loan
Documents (as defined in the Loan Agreement), and Guarantors have guaranteed the
repayment of such Obligations (Borrowers and Guarantors are hereinafter referred
to individually as an "OBLIGOR" and collectively as the "OBLIGORS"); and

            WHEREAS, in order to induce each member of the Lenders to enter into
the Loan Agreement and to effect an equitable sharing of Obligors' risks
thereunder and to establish certain rights and obligations of contribution among
the Obligors with respect to the Secured Obligations (as defined below), each of
the Obligors wishes to enter into this Agreement.

            NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

            1.    DEFINED TERMS. Any and all initially capitalized terms used
herein shall have the meanings ascribed thereto in the Loan Agreement, unless
specifically defined herein.

            (a)   The following terms, as used in this Agreement, shall have the
following meanings:

            "AGREEMENT" shall mean this Contribution Agreement, together with
      any and all future addition, alterations, amendments, changes, extensions,
      modifications, renewals, substitutions, or supplements hereto or hereof.

            "BORROWER" and "BORROWERS" shall have the respective meanings
      ascribed thereto in the recitals hereto.


<PAGE>



            "GUARANTOR" and "GUARANTORS" shall have the respective meanings
      ascribed thereto in the recitals hereto.

            "LENDERS" shall have the meaning set forth in the recitals to this
      Agreement.

            "LOAN AGREEMENT" shall have the meaning set forth in the recitals
      hereto.

            "NET WORTH" shall have the meaning ascribed thereto in Section 2
      hereof.

            "OBLIGOR" and "OBLIGORS" shall have the respective meanings ascribed
      thereto in the recitals hereto.

            "PAYMENT PERCENTAGE" shall have the meaning ascribed thereto in
      Section 2 hereof.

            "SECURED OBLIGATIONS" shall mean all liabilities, obligations, or
      undertakings owing by Obligors to the Lenders of any kind or description
      arising out of or outstanding under, advanced or issued pursuant to, or
      evidenced by the Loan Agreement or any of the other Loan Documents
      irrespective of whether for the payment of money, whether direct or
      indirect, absolute or contingent, due or to become due, voluntary or
      involuntary, whether now existing or hereafter arising, and including all
      interest (including any interest that, but for the provisions of the
      Bankruptcy Code would have accrued) and any and all costs, fees (including
      attorneys fees), and expenses (including any fees and expenses that, but
      for the provisions of the Bankruptcy Code would have accrued) which
      Obligors are required to pay pursuant to any of the foregoing, by law, or
      otherwise.

            (b)   Unless the context of this Agreement clearly requires
otherwise, references to the plural include the singular and to the singular
include the plural, the part includes the whole, the term "including" is not
limiting, and the term "or" has, except where otherwise indicated, the inclusive
meaning represented by the phrase "and/or." The words "hereof," "herein,"
"hereby," "hereunder," and other similar terms in this Agreement refer to this
Agreement as a whole and not exclusively to any particular provision of this
Agreement. Article, section, subsection, exhibits and schedule references are to
this Agreement unless otherwise specified. All of the exhibits or schedules
attached to this Agreement shall be deemed incorporated herein by reference.

            2.    RIGHT OF CONTRIBUTION. If any Obligor makes a payment in
respect of the Secured Obligations that is less than its Payment Percentage (as
calculated below) of the Secured Obligations, then, upon indefeasible payment in
full in cash of the Secured Obligations, the Obligor making such proportionately
smaller payment shall pay to the other Obligors that amount which is necessary
such that the net payments made by all Obligors in respect of the Secured
Obligations are shared among Obligors pro rata according to their respective
Payment Percentages. If any Obligor receives any payment that is greater than
its Payment Percentage (as calculated below) of the Secured Obligations, then
the Obligor receiving such proportionately greater payment shall pay to the
other Obligors that amount which is necessary such that the payments received by
all Obligors shall be shared among all Obligors pro rata according to their
respective Payment Percentages.

                                      -2-


<PAGE>


            Each Obligor's Payment Percentage shall be the percentage calculated
by dividing (a) the Net Worth of such Obligor by (b) the sum of the Net Worth of
all of the Obligors, which Payment Percentage is subject to redetermination or
adjustment as hereinafter set forth. Notwithstanding anything to the contrary
contained herein, (i) the Guarantors shall have no contribution obligations
under this Section 2 unless a Guarantor makes a payment in respect of the
Secured Obligations, and (ii) the Net Worth of each Guarantor shall be included
in the calculation of each Obligor's Payment Percentage only to the extent a
Guarantor makes a payment in respect of the Secured Obligations.

            For purposes of the calculation (and any recalculation) of any
particular Obligor's Payment Percentage, such Obligor's "Net Worth" shall mean
the amount, calculated as of the date such Obligor became a signatory to this
Agreement, by which the sum of all of such Obligor's assets is greater than the
sum of all of such Obligor's debts, at fair valuations, and after giving effect
to the inclusion and exclusion of the matters included and excluded in
determining whether a debtor is insolvent according to Section 548 of Title 11
of the United States Code; PROVIDED, HOWEVER, that for the purpose of
determining the "Net Worth" of any Obligor, no value shall be given to such
Obligor's equity interest in any other Obligor.

            This Section 2 shall constitute a continuing offer to all Persons
who, in reliance upon such provisions, become holders of, or continue to hold,
any of the Secured Obligations, and such provisions are made for the benefit of
the holders of any of the Secured Obligations, and such holders are made
obligees hereunder and any of them may enforce the provisions of this Section 2.

            3.    RIGHT OF CONTRIBUTION CONSTITUTES AN ASSET. Each of the
Obligors hereto acknowledge that the right to contribution hereunder shall
constitute an asset of the Obligor to which such right is owing, but shall not
be considered part of such Obligor's "Net Worth" for the purposes of the
calculation of such Obligor's Payment Percentage pursuant to Section 2 hereof.

            4.    REPRESENTATIONS AND WARRANTIES. Each party hereto represents
and warrants to each other party hereto and to their respective successors and
assigns that:

            (a)   the execution, delivery, and performance by each party hereto
of this Agreement are within such party's powers, have been duly authorized by
all necessary action, require no action by or in respect of, or filing with, any
Governmental Authority and do not contravene or constitute a default under any
provision of law or regulation applicable to it or of the Governing Documents of
such party or of any agreement, judgment, injunction, order, decree, or other
instrument binding upon such party or result in the creation or imposition of
any lien on any asset of such party; and

            (b)   this Agreement constitutes the legal, valid and binding
agreement of each party hereto, enforceable against such party in accordance
with its terms, except as enforcement thereof may be affected by: (i)
bankruptcy, insolvency, reorganization, or other similar laws affecting
enforcement of creditors' rights generally; (ii) general principles of equity
(regardless of whether enforcement is considered in a proceeding in equity or at
law) and (iii) the fact that rights to contribution thereunder may be limited by
federal or state securities laws.


                                      -3-

<PAGE>


            5.    NO WAIVERS; REMEDIES. No failure or delay by any Obligor in
exercising any right, power, or privilege hereunder shall operate as a waiver
thereof nor shall any single or partial exercise thereof preclude any other or
further exercise thereof or the exercise of any other right, power, or
privilege. The rights and remedies herein provided shall be cumulative and
non-exclusive of any rights or remedies provided by law. This Agreement shall
not limit any right which any Obligor may have against any other Person which is
not a party hereto.

            6.    AMENDMENTS. Any provision of this Agreement may be amended or
waived if, but only if, such amendment or waiver is in writing and is signed by
the parties hereto and is made with the consent of the Lenders.

            7.    SUCCESSORS AND ASSIGNS. The provisions of this Agreement shall
be binding upon and inure to the benefit of the parties hereto and their
respective successors and assigns.

            8.    CHOICE OF LAW AND VENUE. THIS AGREEMENT AND THE RIGHTS AND
OBLIGATIONS OF THE PARTIES UNDER THIS AGREEMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.
EACH OBLIGOR AGREES THAT ALL ACTIONS OR PROCEEDINGS ARISING IN CONNECTION WITH
THIS AGREEMENT SHALL BE TRIED AND DETERMINED IN ANY STATE OR FEDERAL COURT OF
COMPETENT JURISDICTION LOCATED IN NEW YORK COUNTY IN THE STATE OF NEW YORK TO
THE MAXIMUM EXTENT PERMITTED BY LAW. EACH OBLIGOR HEREBY EXPRESSLY WAIVES ANY
RIGHT EACH MAY HAVE TO THE DOCTRINE OF FORUM NON CONVENIENS OR TO OBJECT TO
VENUE TO THE EXTENT ANY PROCEEDING IS BROUGHT IN ACCORDANCE WITH THIS SECTION.

            9.    WAIVER OF JURY TRIAL. TO THE MAXIMUM EXTENT PERMITTED BY LAW,
EACH OBLIGOR HEREBY EXPRESSLY WAIVES ANY RIGHT TO TRIAL BY JURY OF ANY ACTION,
CAUSE OF ACTION, CLAIM, DEMAND, OR PROCEEDING ARISING UNDER OR WITH RESPECT TO
THIS AGREEMENT, OR IN ANY WAY CONNECTED WITH, RELATED TO, OR INCIDENTAL TO THE
DEALINGS OF OBLIGORS WITH RESPECT TO THIS AGREEMENT, OR THE TRANSACTIONS RELATED
HERETO, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING, AND IRRESPECTIVE
OF WHETHER SOUNDING IN CONTRACT, TORT, OR OTHERWISE. TO THE MAXIMUM EXTENT
PERMITTED BY LAW, EACH OBLIGOR HEREBY AGREES THAT ANY SUCH ACTION, CAUSE OF
ACTION, CLAIM, DEMAND, OR PROCEEDING SHALL BE DECIDED BY A COURT TRIAL WITHOUT A
JURY AND THAT ANY PARTY MAY FILE AN ORIGINAL COUNTERPART OF THIS SECTION WITH
ANY COURT OR OTHER TRIBUNAL AS WRITTEN EVIDENCE OF THE CONSENT OF THE OTHER
PARTY OR PARTIES TO THE WAIVER OF ITS RIGHT TO TRIAL BY JURY.

            10.   HEADINGS. Headings used in this Agreement are for convenience
of reference only and shall neither constitute a part of this Agreement for any
other purpose nor affect the construction of this Agreement.


                                      -4-


<PAGE>


            11.   NO INCONSISTENT REQUIREMENTS. In the event of a direct
conflict between the terms and provisions contained in this Agreement and the
terms and provisions contained in the Loan Agreement, it is the intention of the
parties hereto that such terms and provisions in such documents shall be read
together and construed, to the fullest extent possible, to be in concert with
each other. In the event of any actual, irreconcilable conflict that cannot be
resolved as aforesaid, the terms and provisions of the Loan Agreement shall
control and govern.

            12.   COUNTERPARTS. This Agreement may be signed in any number of
counterparts, each of which shall constitute an original, and all of which,
taken together, shall constitute one agreement with the same effect as if the
signatures thereto and hereto were upon the same instrument. This Agreement
shall become effective when a counterpart hereof shall have been signed by all
the parties hereto.

                            [signature page follows]



                                      -5-

<PAGE>



            IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement, as of the date first above written.

                                       AMTROL INC.,
                                       a Rhode Island corporation



                                       By:  /s/ Larry T. Guillemette
                                            ---------------------------------
                                            Title: Exec. Vice President & CFO


                                       WATER SOFT INC.,
                                       a Rhode Island corporation



                                       By:  Larry T. Guillemette
                                            ---------------------------------
                                            Title: President



                                       AMTROL HOLDINGS, INC.,
                                       a Delaware corporation



                                       By:  /s/ Albert D. Indelicato
                                            ---------------------------------
                                            Title: President


                                       AMTROL INTERNATIONAL
                                       INVESTMENTS INC.,
                                       a Rhode Island corporation



                                       By:  /s/ Larry T. Guillemette
                                            ---------------------------------
                                            Title: President